When the Arctic Oscillation turns negative, that is, when the winds weaken, the cold air normally trapped around the North Pole surges south.

FORBES: 2011 Forecast: World Outperforms U.S., Europe Scuttles

This pole-centred roundel of warm-in-cold is symptomatic of what climatologists call the negative phase of the Arctic oscillation (AO).

ECONOMIST: Britain��s cold snap is explained by the Arctic oscillation